Low water pressure in one bathroom, other weird occurences

Hello all,

In my master bath, the sink faucet and the shower have always suffered from low water pressure since I bought the house in '05 (house was built in '84). It's a 3 bedroom, 2 bath house on a slab. The other faucets in the house have great water pressure, just the ones in the master bath kinda suck.

Throughout the house, there's also a weird "burst" of higher-pressure water if you turn on the faucet if it hasn't been turned on in a few hours. Then after a few seconds, the water pressure comes back down to normal.

Also, since I am currently replacing the faucet in the master bath, I decided to replace the hoses and valves as well. I had a little extra slack in copper supply piping, so I cut off the old compression ring and about 2 inches of copper tubing. Even though my master water supply valve was totally off, and all faucets in the house were wide open to help bleed pressure out, there was probably 2 gallons of water still trickling out of both hot and cold supply lines.

Any ideas what could be causing this? I hope to God it's not a slab leak, but I don't really have any other slab leak symptoms (hot or cold floors, trickling sounds, etc). Thanks.

I would check the aerator on the faucet for debris and unscrew the showerhead from the showerarm to check the restrictor in that as well.

As for the burst of pressure I'm going to guess that you have a Pressure Reducing Valve (PRV) or, a check valve installed. The PRV may be bad allowing pressure to creep higher, or, there may be a problem with thermal expansion and a thermal expansion tank sould be installed or, replaced.
A litle bit of troubleshooting and more information is needed on that subject.

Aerator was fine on the old faucet, and I assume fine on the new one (haven't installed it yet). Shower head has been replaced recently, it's fine too.

The PRV is something I need to check, or need to have checked, since most plumbers like to recommend plumbers do this type of stuff instead of homeowners. I do have a thermal expansion tank on my hot water heater, replaced a year ago.. does that count?

Thanks for the help.

Yes it does and hopefully is still okay.
I would use a pressure gauge to see if the pressure is set right, if it is creeping up while the water heater is not heating, if it is creeping up while the water heater is heating.